Make sure you buy decent rims on the snow tires, and not cheapo ones.
If you live in the city then there shouldn't be a problem.
But, if you have a cottage in snowbound areas, or like to go to ski resorts, then I'd invest on an X5 as a winter car.
My general rule is that if the accumulation of snow gets past 3 inches, park the M. But, I've driven the car through blizzards before....very, very carefully.
It helps that the car terrific road feel, and will let you know when you're about to end up in a ditch.
It's not an ideal winter car, but good snow tires + careful driving and you should be able to get by with the M. :rocks: